A. Field Of The Invention
The present invention relates generally to fiber-optic devices and more particularly to single-mode, fiber optic power dividers and means for tuning thereof.
B. Description Of The Prior Art
Single-mode optical fibers are currently used in high-capacity information systems and communications applications to transmit high-frequency signals. It is frequently necessary in such applications to join single-mode fibers or couple a multiplicity of fibers in order to modify the transmittal characteristics of a particular fiber system. Sheem and Giallorenzi, 4 Optics Letters, No. 10 (Oct. 1979) pg. 29, describe a single-mode fiber-optic power divider which consists of a pair of optical fibers encased in a housing. The Sheem et al. housing has a threaded cap at one end which may be manipulated to increase or decrease tension in the fibers during fabrication. One disadvantage of the device described by Sheem et al. is that the threaded cap must be machined and precisely threaded to fit the housing, generally made of quartz, on which it is used. Another disadvantage of the Sheem et al. device is that increased tension in the fibers can cause longitudinal and axial stress to build up in the fibers. This may enhance breakage. Conversely, slackening of the fibers, to reduce tension, results in increased optical losses and decreased coupling efficiency. From a practical point of view, a most important disadvantage of the Sheem device is that the threaded cap arrangement may only be used to adjust coupling characteristics during the fabrication stage of the device because the final stage of fabrication is to fill the device with a material which polymerizes within the housing to form a solid. Once the device has been fabricated, it is no longer possible to adjust its optical characteristics because attempts to adjust the threaded cap will easily strain the fibers and break them.